Stabilizing open graded asphalt-concrete

ABSTRACT

A method is provided for stabilizing an open graded course of asphalt-concrete against lateral displacement under a moving load. The method which is suitable for use during construction of the asphalt-concrete course or on courses already completed is carried out by causing particulate matter of suitable size to be passed into the interstices of the asphalt-concrete course and then consolidating this particulate matter within the interstices using an emulsion of a thermoplastic elastomer, a resinous material and a polar solvent which upon curing forms a stabilized course.

United States Patent Bennett et al.

[ 1 Sept. 23, 1975 Dale F. Levy, all of Bartlesville, Okla.

[73] Assignee: Phillips Petroleum Compan Bartlesville, Okla.

[22] Filed: Aug. 28, I974 [21] Appl. No.: 501,203

[52] US. Cl. 404/75; 404/72; 404/77 [5 l] Int. Cl. E01C 7/06 [58] Field of Search 404/l7, 72, 75, 77

[56] References Cited UNITED STATES PATENTS 851,625 4 1907 llassam 404/72 987,726 3/191 1 Lassailly 404/72 l2/l950 6/l963 Martin 404/75 Gessler 404/17 Primary E.\'uminerMervin Stein Assistant Examiner-Steven Hawkins [57] ABSTRACT v A method is provided for stabilizing an open graded course of asphalt-concrete against lateral displacement under a moving load. The method which is suitable for use during construction of the asphaltconcrete course or on courses already completed is carried out by causing particulate matter of suitable size to be passed into the interstices of the asphaltconcrete course and then consolidating this particulate matter within the interstices using an emulsion of a thermoplastic elastomer, a resinous material and a polar solvent which upon curing forms a stabilized course 8 Claims, No Drawings STABILIZING OPEN GRADED ASPHALT-CONCRETE BACKGROUND OF'THE INVENTION An o pengraded course of asphalt-cement a ggregate mix is a thin, porous layer of aggregate one-half inch to two inches, more commonly three-fourth inch mom and one-half inches, thick after compaction, designed to allow rapid drainage of rain water from ,a paved surface. Since this surface is especially designed to prevent the buildup of water layers which might lead to hydroplaning conditions, these surfaces are usually I foundon roadways but are more especially useful in airport aprons and runways.

These pavements have intersticial voids and are not as'compact as the underlying bearing surface so that the impact and rolling motion of a large vehicle, such as a large plane, tend to displace the open graded overlay thereby producing hills and valleys along a paved area such as a' runway or airport apron. This can become a problem on roadways at intersections where large trucks are caused to stop but is an especially aggravated problem in the turning area of multi-wheeled planes. we have found that the problem of lateral displacement or shoving of an asphalt-concrete course under a moving load can be alleviated by a two-step treatment of an open graded course of an asphaltcement aggregate either atthe time of construction or after the pavementis set and a problem of displacement has been noticed.

Other aspects and the several advantages of this invention will be apparent to those skilled in the art upon reading the disclosure and the appended claims to this invention.

SUMMARY OF THE INVENTION Accordingly, a method is provided for stabilizing an open graded course of asphalt-concrete against lateral displacement under a moving load. The method comprises first causing particulate matter to be passed into the interstices of the asphalt-concrete course and then consolidating the particulate matter within the interstices using an emulsion comprising a thermoplastic elastomer, a resinous material and a polar solvent.

In one embodiment of the invention an open graded course of asphalt-concrete stabilized against lateral displacement under a moving load is provided. The stabilized course is composed of an open graded course of asphalt-concrete, particulate. matter within the interstices of the course, and a cohering material comprising a cured composition of a thermoplastic elastomer and a resinous material consolidating the particulate matter within the interstices.

' DESCRIPTION OF THE PREFERRED EMBODIMENTS By the method of this invention any of the types of particulate matter having sufficient strength to be used in paving construction when reduced to a size capable of entering the interstices of an open graded course of asphalt-concrete is suitable for use in this invention.

The most common particulate material suitable for this use is sand. The sand or other particulate material should be'of a' size of mesh or finer to be able to enter the interstices. Since the drainage characteristics of the asphalt-cement course are sought to be retained.

it is preferred that a lower 'li'mit'of particle size should be not less than 200 mesh.

The particulate matter-is applied at a rate of about 2 toabout 5 pounds per square yard ofsurface. preferably from about 3 pounds to about 4 pounds pe'rsquare yard of surfacerA bro'om or rotary brush'can be used to distribute the-sand across the surface and cause it to enter the interstices of the asphalt-concrete course. Another method.- for insinuating-the particulate matter into the interstitial space of the asphalt-concrete course is to vibrate the pavementJThevibration will cause the particulate matter to siftinto the interstices. The p'avement can be vibrated-by a suitable device such as a vibrating roller. lf'the open' graded layer is exceptionally deep, i.e., above l.51inches. a combination of the brushing and vibrating methods can be used.

After the particulate matter has been insinuated into the structure of the asphalt-concrete pavement. the pavement is treated with a rock binding emulsion of solvent-water and rubber. This emulsion penetrates into the pavement and deposits a small cementing quantity of high green strength rubber at the contact points of the particles. This deposition at the contact points is sufficient to cohere the particles but'not sufficient to interfere with the porosity of the structure. In this way the pavement is not sealed or made sufficiently impermeable to interfere with runoff of water from the surface. To maintain this balance of properties the solvent-water-rubber emulsion is sprayed on the'pavement at a rate of about 0.2 to about l.5gallons per square yard of surface, preferably from about 0.3 to about 0.75 gallons per square yard of surface.

The preferred elastomeric bonding agent is a thermoplastic elastomer of the block copolymer type, or of the trans-diene polymer type. or a blend of the two polymers. An informative paper on the influence of structure and composition on properties of block copoly- I mers has been published by Childers and Kraus in Rubber .Chemistry and Technology.

40 I 183-] I99 (September, I967). Since no claim is made to the polymersper se. and since they have been described in the prior art, it will be sufflcient to refer to the aboveeited literature and also to U.S. Pat. Nos.

. by Childersand Kraus.

We prefer to use the poly(styrene)-poly(butadiene-)- poly(styrene) block copolymers having the conjugated diene blocks of molecular weight between 2,000 and 1,000,000, and the end blocks having a molecular weight between 2,000. and 100,000.

Other block copolymers such as poly(styrene)- poly(acrylonitrile)-poly(styrene), poly(isoprene)-poly(styrene or other combinations of plastic elastic block polymers may also be used; Those skilled in the art will also be able to substitute, for block copolymers, graft polymers or polymers stiffened by poly(styrene)- incorporation oforganic fillers as long as this fulfills the requirements of the characteristics for which the block copolymers are chosen in accord with the present invention, i.e.. capable of developing material strength without the step of vulcanization by heat.

The elastomers may be stiffened by adding a stiffening resin in the form, for example, of an amorphous resin. A suitable stiffening resin may be a polymer of styrene or coumarone-indene resin. The resin should have properties which are similar to those of the coumarone-indene type, and resins derived from coal tar or petroleum can be used. The preferred softening point range of the amorphous resin is from about l40 to 300F. The main characteristics of the resin are that it is compatible with the block copolymer, is amorphous, and does not possess the elastomeric properties I of being extensible and retractable.

An extender oil, such as commonly used in rubber compounding and described in ASTM Method D22226, Description of Types of Petroleum Extender Oils. may also be used. The use of extenders is well known. However, it is preferred to use a minimum concentration of such extender oil which will produce the desirable qualities of the composition set forth herein, and preferably to omit such oil entirely.

The preferred elastomeric bonding agent, modified as desired by the addition ofa stiffening resin, or an extender, or both, may be applied dissolved in a volatile solvent or applied in the form of an emulsion. Antioxidants and antiozonants, such as commonly used to inhibit the attack of oxygen and ozone on rubber compounds, may be added to the composition to improve the aging properties of the binder.

The polymer may be applied to the aggregate as a dispersion, either as solution in a solvent or as an emulsion. Suitable solvents are low boiling, e.g., below about l25C, chlorinated hydrocarbons. such as trichloroethylene, and aromatic solvents such as benzene. toluene, and xylene. Coal tar naphthas containing these chemicals may also be used. One skilled in the art may select various suitable solvents or azeotropes from those listed in the literature, e.g., Solvenls Guide. by Marsden and Mann (Cleaver-Hume Press Ltd.. London). Compositions suitable for use in this procedure are described in US. Pat. No. 3,788,883 (F. S. Rostler ct al. Jan. 29, l974), herein incorporated by reference and more specifically described in the example which follows below.

The preferred cohering material used in this invention is an emulsion comprising thermoplastic elastomer of a butadiene-styrene block copolymer type dissolved in a suitable solvent, a resinous material. and a polar solvent substantially as described above, sold by Phillips Petroleum Company under the tradename Petroset RB. This material produces a bonding agent which. without vulcanization, has, as shown by standard stress strain tests, more than ten times the strength of conventional rubbers.

The method for bonding the particulate matter is as follows. The particulate matter containing pavement is washed with water and allowed to drain. The Petroset emulsion is then sprayed on the particulate matter and breaks" thereby depositing the cementing agent at these points of contact. After a few hours, the cementing agent develops into small, individual elastomeric vibration pads at the points of contact which weld the treated particulate matter into an elastomeric consolidated structure. It has been found that heat can be used to cure the consolidated structure more rapidly; preferably steam or hot air is used in such curing process.

Additionally, it has been found that it is sometimes useful after the particulate matter containing pavement has been washed with water and allowed to drain that it can be sprayed with a dilute alkaline solution of concentration range of approximately 0.5 to 5 percent, preferably 1 to 3 percent, and allowed to drain again. The dilute alkaline solution can be selected from solutions of sodium hydroxide, sodium bicarbonate, sodium carbonate and preferably ammonia. Part of the solution is held between the individual particles by capillary forces at the points where the particles come into contact with each other. Upon spraying Petroset emulsion onto the particulate matter, contact with the alkaline solution held at the points where one particle contacts another in the interstices of the pavement causes the emulsion to break depositing the cementing agent at the points of contact. The addition of this step to the process helps to assure better bonding of individual particles.

The following example is a test which was made at a commercial airport. This test illustrates an embodiment ofthe invention to show its operativeness and should be taken as illustrative and not exclusive.

EXAMPLE Aggregate Percent Sieve Size Passing 9%" I00 95 No. 4 44 No. l6 l2 No. 200 2 This had been mixed with 6 percent by weight of a bituminous binder and applied at 240F. The course had been laid and had been in service for about 1 year.

About 34 pounds of 70-mesh sand were applied, using hand brooms to distribute the sand evenly into the void space; the final amount of sand in place was estimated at 23 lbs./sq. yard.

Area 1: Solvent-watcr-rubber emulsion was diluted with two parts of water and applied at 0.5 gaL/sq. yd.

Area 2: Was first wctted with fine water spray and then l:2 emulsion: water was applied at the rate of 0.5 gaL/sq. yd.

Area 3: Same as Area 1 but dilution ratio was l:l.

Area 4: Same as Area 2 with dilution ratio lzl.

The undiluted solvent-water-rubber solution had the following composition:

-Continued 7: Ingredient Wt Xylene 16.6 Cyanox SS 0.3 Nickel dibutyldithiocarhamate 0.3 507: Hyamine 2389 2.0 Redicote E-l-" 0.5 31.57: HCl 0.45 Methanol 2.0 Water 20.05

'Solprene 4l4. Phillips Petroleum Company. Neville Resin Rl6A. Neville Manufacturing Co. '22'methylene-his-l4-methyl-6 tert hutyl phenol] American Cyanamid Corp.

"Mcthyldodecylhenzyl trimelhyl ammonium chloride and methyldodecyl xylene histtrimethyl ammonium chloride). cationic emulsifier Rohm 84 Haas. """lallow Diamines Armour Industrial Chemicals.

Four days after applying the treatment, the test sites were inspected and all areas were stabilized. Cores were obtained and showed that Sections l and 2 had the deepest penetration of the rubber emulsion (dilution ratio 1:2) into the open graded layer. Another inspection, about 2 weeks later, showed no deformation of the treated section, no loss of aggregate, no rutting. The area was still in good shape 6 months later.

Reasonable variation and modification are possible within the scope of the foregoing disclosure and the appended claims the essence of which is that an open graded course of asphalt-concrete can be stabilized against lateral displacement under a moving load by insinuating fine particulate matter into the interstices of the pavement and consolidating the particulate matter with a rubber emulsion treatment without softening the asphaltic or bituminous component of the asphaltcementaggregate mix so that the structural integrity of a relatively thin top layer of pavement can be improved without affecting the bearing courses of pavement beneath this top layer of specialized construction.

We claim:

1. A method for stabilizing an open graded course of asphalt-concrete against lateral displacement under a moving load. said method comprising:

1. causing particulate matter to he passed into the interstices of said asphalt-concrete course. said particulate matter sized in a range sufficiently small to enter the interstices. and

2. consolidating the particulate matter within the interstices with an emulsion comprising a thermoplastic elastomer. a resinous material. and a polar solvent.

2. The method of claim 1 wherein particulate matter is caused to pass into said interstices by brushing the particulate matter over the surface of the course. vibrating the particulate matter into the surface of the course. or combining brushing and vibrating operations.

3. The method of claim 1 wherein the particulate matter is sand applied at a rate of about two to about five pounds per square yard of surface area.

4. The method of claim 1 wherein consolidating with said emulsion comprises:

1. wetting the particulate matter with said emulsion.

2. allowing the emulsion to break. and

3. allowing the resulting elastomeric. consolidated structure to cure.

5. The method of claim 4 wherein the particulate matter within said interstices is wetted with a dilute alkaline solution selected from sodium hydroxide. sodium bicarbonate, sodium carbonate and ammonia and excess of said solution is allowed to drain prior to wetting the particulate matter with said emulsion.

6. The method of claim 4 wherein curing is effected by applying heat to the treated asphalt-concrete course.

7. The method of claim 6 wherein the heat is applied using steam.

8. The method of claim 6 wherein the heat is applied using hot air. 

1. A METHOD FOR STABILIZING AN OPEN GRADED COURSE OF ASPHALT-CONCRETE AGAINST LATERAL DISPLACEMENT UNDER A MOVING LOAD, SAID METHOD COMPRISING:
 1. CAUSING PARTICULATE MATTER TO BE PASSED INTO THE INTERSTICES OF SAID ASPHALT-CONCRETE COURSE, SAID PARTICULATE MATTER SIZED IN A RANGE SUFFICIENTLY SMALL TO ENTER THE INTERSTICES, AND
 2. CONSOLIDATING THE PARTICULATE MATTER WITHIN THE INTERSTICES WITH AN EMULSION COMPRISING A THERMOPLASTIC ELASTOMER, A RESINOUS MATERIAL, AND A POLAR SOLVENT.
 2. consolidating the particulate matter within the interstices with an emulsion comprising a thermoplastic elastomer, a resinous material, and a polar solvent.
 2. The method of claim 1 wherein particulate matter is caused to pass into said interstices by brushing the particulate matter over the surface of the course, vibrating the particulate matter into the surface of the course, or combining brushing and vibrating operations.
 2. allowing the emulsion to break, and
 3. allowing the resulting elastomeric, consolidated structure to cure.
 3. The method of claim 1 wherein the particulate matter is sand applied at a rate of about two to about five pounds per square yard of surface area.
 4. The method of claim 1 wherein consolidating with said emulsion comprises:
 5. The method of claim 4 wherein the particulate matter within said interstices is wetted with a dilute alkaline solution selected from sodium hydroxide, sodium bicarbonate, sodium carbonate and ammonia and excess of said solution is allowed to drain prior to wetting the particulate matter with said emulsion.
 6. The method of claim 4 wherein curing is effected by applying heat to the treated asphalt-concrete course.
 7. The method of claim 6 wherein the heat is applied using steam.
 8. The method of claim 6 wherein the heat is applied using hot air. 